The field of application of the invention is particularly that of gas turbine aeroengines. Nevertheless, the invention is applicable to other turbine engines, e.g. industrial turbines.
Ceramic matrix composite (CMC) materials are known for conserving their mechanical properties at high temperatures, which makes them suitable for constituting hot structural elements.
In gas turbine aeroengines, improving efficiency and reducing certain polluting emissions lead to a search for operation at ever-higher temperatures. For turbine ring assemblies made entirely out of metal, it is necessary to cool all of the elements of the assembly, and in particular the turbine ring, which is subjected to streams that are very hot, typically hotter than the temperature that can be withstood by the metal material. Such cooling has a significant impact on the performance of the engine, since the cooling stream used is taken from the main stream through the engine. In addition, the use of metal for the turbine ring limits possibilities for increasing temperature within the turbine, even though that would improve the performance of aeroengines.
Furthermore, a metal turbine ring assembly deforms under the effect of hot streams, thereby changing clearances associated with the flow passage, and consequently modifying the performance of the turbine.
That is why proposals have already been made to use CMC for various hot portions of engines, particularly since CMCs present the additional advantage of density that is lower than that of the refractory metals conventionally used.
Thus, making turbine ring sectors as single pieces of CMC is described in particular in Document US 2012/0027572. The ring sectors have an annular base with its inner face defining the inside face of the turbine ring and an outer face from which there extend two tab-forming portions having their ends engaged in housings in a metal ring support structure.
The use of ring sectors made of CMC makes it possible to reduce significantly the amount of ventilation needed for cooling the turbine ring. Nevertheless, keeping or retaining ring sectors in position remains a problem in particular in the face of differential expansion, as can occur between a metal support structure and CMC ring sectors. In addition, another problem lies in controlling the shape of the passage both when cold and when hot without generating excessive stresses on the ring sectors.